1. Technical Field of the Invention
The present invention relates to a method of manufacturing a cylindrical container using a metal sheet on at least one surface of which the metal is exposed.
2. Description of the Related Art
When a metal sheet is drawn into a cylindrical shape, blanks punched out to circular sheets have heretofore been used. However, when blanks such as circular sheets are punched out of an elongate rolled metal sheet, even though the blanks to be punched out are arranged in a staggered manner so that an unnecessary portion between adjacent blanks is the least, a problem arises in that the unnecessary portion, which includes approximately triangular shapes, inevitably remains as a scrap portion to reduce the yield rate. In view of this, Patent Document 1 (PCT International Publication No. WO 98/51426) proposes a technique of punching out the blanks into a hexagonal shape in order to reduce the occurrence of such a scrap portion.
If the blanks are formed into a hexagonal shape, however, another problem may arise in that portions (earings) higher in container height than the other portions readily occur due to the effect of corner parts of the blank when the drawing process is performed, compared to the case of circular shape. In view of this, Patent Document 2 (PCT International Publication No. WO 99/48631) discloses a method in which, when the drawing process is performed using a hexagonally-shaped blank formed of a resin coated steel sheet having a resin layer, a die for drawing process is used which has groove-formed areas, each having a plurality of grooves, at certain portions of a wrinkle preventing surface, wherein the certain portions correspond to the corner parts of the hexagonal shape.